Communication method and device

ABSTRACT

This application provides a communication method and a device. The method includes: sending, by a terminal device to a network device, a random access preamble, receiving, by the terminal device, a random access response (RAR) from the network device, wherein the RAR indicates a first resource, and sending, by the terminal device, downlink channel quality indication information to the network device, wherein the downlink channel quality indication information is carried in a Message  3  on the first resource, and the downlink channel quality indication information is used to indicate downlink channel quality.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/721,198, filed on Dec. 19, 2019, which is a continuation ofInternational Application No. PCT/CN2017/089560, filed on Jun. 22, 2017.All of the aforementioned patent applications are hereby incorporated byreference in their entireties.

TECHNICAL FIELD

This application relates to the communications field, and in particular,to a communication method and a device.

BACKGROUND

Machine type communication (machine type communication, MTC), which mayalso be referred to as machine-to-machine (machine to machine, M2M)communication, or the internet of things (internet of things, IoT) is animportant future application in the communications field. Futureinternet-of-things communication may mainly cover smart metering,medical detection and monitoring, logistics detection, industrialdetection and monitoring, the internet of vehicles, intelligentcommunities, wearable device communications, and the like. Aninternet-of-things industry constructed based on MTC is considered as afourth tide following computers, the internet, and mobile communicationsnetworks in the information industry, and is a future networkdevelopment trend.

A type of important MTC communications system is a communications systembased on an existing cellular network infrastructure, and this type ofMTC is usually referred to as cellular MTC (cellular MTC) or a cellularIoT (cellular IoT, CIoT). Currently, a cellular MTC service mainly posesthe following requirements on a network and a terminal device:

Requirement for wide coverage: A current visible MTC service usuallydoes not need a quite high service rate, but needs a capability tosupport wide coverage. Wide coverage means that an MTC base station hasa relatively strong coverage enhancement technology, and is capable ofproviding a communications service for user equipment in a case of arelatively high penetration loss (for example, 164 dB). For example,user equipment in a smart home or smart metering service, such as asmart water/electricity meter, is usually installed indoors or even in abasement. It is hard to provide a reliable communications service fordevices at these locations by using an existing cellular networktechnology, whereas the MTC base station needs to provide a robustconnection service for such devices.

Extremely large quantity of connections: For internet-of-things terminaldevices deployed on a large scale, such as smart water/electricitymeters, intelligent communities, monitoring devices, vehicles, andwearable devices, there may be a large quantity (more than tens ofthousands or even hundreds of thousands) of such terminal devices servedby one MTC base station, and the quantity is far greater than a quantityof existing mobile terminals. How a connection service is provided forsuch an enormous quantity of terminal devices at a same moment whilenetwork congestion is avoided is a problem that needs to be resolved.

Low costs (low costs): Costs of an MTC terminal device need to be lowerthan costs of an existing mobile terminal, and the low costs are aprerequisite for massively deploying MTC terminal devices.

Low power consumption (low power consumption): Because of diversity ofactual application of an MTC terminal and various deploymentenvironments, power is usually supplied to the MTC terminal device byusing a battery. If batteries need to be replaced for such an enormousquantity of devices, extremely high manpower and time costs are paid. AnMTC device usually requires an extremely low power consumption level forits functional components, so that the device can have a longer standbytime, thereby reducing a quantity of battery replacement times.

The 3rd Generation Partnership Project (3rd generation partnershipproject, 3GPP) standards organization has been focusing on developmentof cellular MTC and actively carries out standardization of relatedtechnologies, for example, holds discussions related to a narrowband IoT(narrowband IoT, NB-IoT) system.

Because an NB-IoT system needs to support a quite large coverage area,for terminal devices in different communication environments, schedulingpolicies of a network device are totally different. For example, aterminal device at a central location of a cell has a desirable radiochannel condition, and the network device can establish a reliabledownlink by using only relatively low power, and can quickly completedata transmission by using technological means, such as a largetransport code block, higher-order modulation, and carrier binding.However, a terminal device at the edge of the cell or in a basement hasrelatively poor radio channel quality, and the network device canmaintain a link in need of relatively high power and can complete datatransmission in a data transmission process by using technical means,such as a small code block, lower-order modulation, repeated sending fora plurality of times, and the spread spectrum.

To ensure communication reliability and reduce transmit power of thenetwork device, terminal devices in different channel conditions need tobe distinguished, to help the network device perform scheduling. In viewof this, a concept “coverage level” is introduced in the NB-IoT system.Channel transmission conditions of terminal devices at a same coveragelevel are similar. The network device may use a similar schedulingparameter for such users, and control signaling overheads occupied bythe users are also similar. For example, in the NB-IoT system, threecoverage levels may be obtained in the downlink through classification.A coverage level of a terminal device relatively close to the networkdevice is “common coverage” (for example, a coverage level 0), and aquantity of repetition times is 0. A coverage level of a terminal devicerelatively far away from the network device is “edge coverage” (forexample, a coverage level 1), and a quantity of repetition times is 8 or16. A coverage level of a terminal device in a scenario such as in abasement is “extended coverage” (for example, a coverage level 2), and aquantity of repetition times may be up to 32, 64, or greater. A terminaldevice selects a proper quantity of preamble (preamble) transmissiontimes based on a coverage level, so that a quantity of unnecessaryrepetition times and power overheads can be reduced.

Currently, a coverage level in NB-IoT is a specific coverage leveldetermined after the terminal device compares a downlink referencesignal received power (reference signal received power, RSRP)measurement value with an RSRP threshold preconfigured by the networkdevice. Specifically, the network device provides, in system message,RSRP decision thresholds of different coverage levels. The terminaldevice determines a corresponding coverage level based on a result ofcomparison between an RSRP and a decision threshold, and sends apreamble (preamble) on a narrowband physical random access channel(narrowband physical random access channel, NPRACH) resourcecorresponding to the coverage level. For a preamble corresponding to aminimum quantity of repetition times, the terminal device first sendsthe preamble by using relatively low power. If the sending fails, theterminal device increases its transmit power. For a preamblecorresponding to another quantity of repetition times, the terminaldevice transmits the preamble by using maximum power.

From a perspective of a network device, the network device detectspreambles on all NPRACH resources. Once the network device detects apreamble sent by a terminal, a coverage level of the terminal isdetermined based on a resource on which the detected preamble islocated, and a quantity of repetition times of a downlink narrowbandphysical downlink control channel (narrowband physical downlink controlchannel, NPDCCH) is determined based on a magnitude of the estimatedcoverage level. A random access response (random access response, RAR)is further scheduled on the NPDCCH and fed back to the terminal device.

Based on the foregoing description, in the existing NB-IoT system, if aterminal device fails in performing access at a coverage level 0, theterminal device switches to a coverage level 1 for random access.According to an existing protocol, the terminal device needs to send apreamble by using maximum power. In this case, the terminal device isstill at the coverage level 0 actually, and is relatively close to anetwork device. Therefore, if the preamble is sent by using the maximumpower, a noise floor of a receiver of the network device is increased,affecting random access of a terminal device at another higher coveragelevel.

SUMMARY

Embodiments of this application provide a communication method and adevice, to reduce impact on another terminal device.

According to a first aspect, a communication method is provided, wherethe method includes:

determining, by a terminal device, a current coverage level from atleast two coverage levels, where each of the at least two coveragelevels is corresponding to a power ramp step; and

sending, by the terminal device to a network device in a power rampingmanner based on a power ramp step corresponding to the current coveragelevel, a random access preamble.

Therefore, in this embodiment of this application, the terminal devicesends the preamble at the current level by using power determined in apower ramping manner, and a prior-art manner of directly sending apreamble by using maximum power is abandoned. This can reduce impact onanother terminal device.

It should be understood that the power ramp step indicates a powerincrease amplitude when the terminal device resends a preamble afterfailing in sending the preamble at the current coverage level.

It should be understood that, in this embodiment of this application,after the terminal device sends a preamble, if no RAR is received, itindicates that the sending fails; or when the terminal device receivesan RAR but the RAR does not include the sent preamble, it also indicatesthat the sending fails.

Optionally, in an implementation of the first aspect, the terminaldevice determines the current coverage level from the at least twocoverage levels based on reference signal received power.

Optionally, in an implementation of the first aspect, the terminaldevice determines the current coverage level from the at least twocoverage levels based on reference signal receiving performance.

Optionally, in an implementation of the first aspect, the determining,by the terminal device, the current coverage level from the at least twocoverage levels based on reference signal receiving performanceincludes:

determining, by the terminal device, an initial coverage level based onthe reference signal received power; and

when the initial coverage level does not match the reference signalreceiving performance, determining, by the terminal device, a coveragelevel corresponding to the reference signal receiving performance as thecurrent coverage level.

For example, when the initial coverage level corresponding to thereference signal received power is a coverage level N, and the referencesignal receiving performance is corresponding to a coverage level N+1,the terminal device determines that the current coverage level is thecoverage level N+1; or when the initial coverage level corresponding tothe reference signal received power is a coverage level N, and thereference signal receiving performance is corresponding to a coveragelevel N+2, the terminal device determines that the current coveragelevel is the coverage level N+2.

Optionally, in an implementation of the first aspect, the sending, bythe terminal device to a network device in a power ramping manner basedon a power ramp step corresponding to the current coverage level, arandom access preamble includes:

when failing in sending the preamble last time, increasing, by theterminal device, transmit power of the preamble by the current powerramp step corresponding to the current coverage level, to obtain newpower; and resending the preamble by using the new power.

It should be understood that, in this embodiment of this application,sending a preamble once indicates sending the preamble based on aquantity of repetition times corresponding to the current coveragelevel.

When sending for the first time fails, the terminal device resends thepreamble after increasing first-time power by a power ramp step. Othercases are by analogy with the foregoing. Optionally, in actualapplication, the terminal device may determine, based on target receivedpower of the preamble and a path loss between the terminal device andthe network device, the transmit power of the preamble, where the targetreceived power of the preamble is related to the current power ramp stepand a current quantity of times of sending the preamble by the terminaldevice.

Optionally, the transmit power of the preamble is determined by theterminal device according to the following formula:

P _(NPRACH)=min{P _(CMAX) , P _(TARGET) +PL} [dBm], where

P_(NPRACH) represents the transmit power of the preamble,P_(CMAX)represents maximum transmit power of the terminal device, P_(TARGET)represents the target received power of the preamble, and PL representsthe path loss, where

P_(TARGET)=P_(P)+(M−1)P_(s), where

P_(P) represents initial target received power of the preamble, Mrepresents the current quantity of sending times, and P_(S) representsthe current power ramp step; or

P_(TARGET)=P_(P)+(M−10) P_(S)−10×log₁₀N_(r) , where N_(r) is a quantityof repetition times of sending the preamble.

It should be understood that, in this embodiment of thisapplication,P_(CMAX) is a parameter P_(CMAX, c) ^((i)) in a protocol andindicates maximum transmit power of the terminal device in a servingcell c in an NB-IoT uplink slot i, P_(TARGET) is a parameterNARROWBAND_PREAMBLE_RECEIVED_TARGET_POWER in the protocol or P_(TARGET)is a parameter PREAMBLE_RECEIVED_TARGET_POWER in the protocol, PL is aparameter PL_(c) in the protocol and indicates a downlink path loss,P_(P) is a parameter preamblelnitialReceivedTargetPower in the protocol,M is a parameter PREAMBLE_TRANSMISSION_COUNTER in the protocol, andN_(r) is a parameter numRepetitionPerPreambleAttempt in the protocol.

It should be understood that the foregoing formula is only a specificform of determining the transmit power, and variation may be performedappropriately based on the foregoing formula. This embodiment of thisapplication is not limited thereto.

Optionally, in an implementation of the first aspect, the method furtherincludes:

when a quantity of times of sending the preamble by the terminal deviceat the current coverage level is greater than a first threshold,sending, by the terminal device, the preamble to the network device at anext coverage level of the current coverage level, where

the first threshold is less than a maximum quantity of times oftransmitting a preamble at each coverage level.

In this case, in this embodiment of this application, when the quantityof times of sending the preamble at the current coverage level isgreater than the first threshold, coverage level switching may beperformed. Because the first threshold is less than the maximum quantityof times of transmitting a preamble, when current channel quality isrelatively poor, a quantity of unnecessary failures at the currentcoverage level can be reduced. This reduces a resource waste andimproves network performance.

Optionally, in an implementation of the first aspect, the sending, bythe terminal device, the preamble to the network device at a nextcoverage level of the current coverage level includes:

sending, by the terminal device, the preamble in a power ramping mannerby using a quantity of repetition times corresponding to the nextcoverage level and the current power ramp step corresponding to thecurrent coverage level.

Therefore, in this embodiment of this application, during levelswitching, the terminal device still sends the preamble by using powerdetermined in a power ramping manner, and a prior-art manner of directlysending a preamble by using maximum power is abandoned. This can reduceimpact on another terminal device. In addition, after the levelswitching, although the transmit power is determined in a previous powercontrol manner, the preamble is sent based on the quantity of repetitiontimes corresponding to the next coverage level, so that a quantity ofrepetition times of the preamble during each transmission can beincreased, thereby improving an access success probability.

Optionally, in an implementation of the first aspect, the method furtherincludes:

receiving, by the terminal device, indication information sent by thenetwork device, where the indication information is used to indicate aquantity of repetition times of sending uplink information by theterminal device; and

when the terminal device determines that the quantity of repetitiontimes is greater than a second threshold, sending, by the terminaldevice, the uplink information by using maximum transmit power; or

when the terminal device determines that the quantity of repetitiontimes is less than or equal to the second threshold, sending, by theterminal device, the uplink information by using first power, where thefirst power is determined by the terminal device based on at least oneof a path loss, a path loss compensation factor, or transmissionbandwidth.

Optionally, in an implementation of the first aspect, the indicationinformation is carried in an uplink grant UL grant, and the uplinkinformation is uplink data; or the indication information is carried ina random access response RAR, and the uplink information is a Message 3.

Optionally, in an implementation of the first aspect, the secondthreshold is preset, the second threshold is indicated by the RAR, orthe second threshold is configured by using a system message.

Optionally, in an implementation of the first aspect, the method furtherincludes:

when the terminal device detects that a coverage level corresponding todownlink channel quality does not match the current coverage level,re-initiating, by the terminal device, a random access procedure at thecoverage level corresponding to the downlink channel quality.

Specifically, after the terminal device completes a random accessprocedure, that is, when the terminal device performs data transmissionwith the network device, if the terminal device detects that thecoverage level corresponding to the downlink channel quality does notmatch the current coverage level, the terminal device re-initiates therandom access procedure based on the coverage level corresponding to thedownlink channel quality, and then performs data transmission after there-initiated random access procedure is completed.

Optionally, in an implementation of the first aspect, the method furtherincludes:

sending, by the terminal device, downlink channel quality indicationinformation to the network device, where the downlink channel qualityindication information is carried in a Message 3 sent by the terminaldevice, and the downlink channel quality indication information is usedto indicate downlink channel quality.

Optionally, in an implementation of the first aspect, the sending, bythe terminal device, downlink channel quality indication information tothe network device includes:

sending, by the terminal device, the downlink channel quality indicationinformation to the network device based on an indication ofconfiguration information, where the configuration information iscarried in an RAR sent by the network device, or the configurationinformation is carried in a system message.

Optionally, in an implementation of the first aspect, the downlinkchannel quality indication information includes reference signalreceived quality RSRQ, or a quantity of NPDCCH repetition times duringRAR demodulation by the terminal device.

Therefore, in this embodiment of this application, the terminal devicereports the downlink channel quality, so that the network device canproperly determine a maximum quantity of repetition times of sending aMessage 4 and/or a maximum value of a UE-specific search space(UE-specific search space, USS) of the terminal device based on thedownlink channel quality. This resolves an existing problem and avoidsexcessive power consumption of the terminal device and a system resourcewaste, thereby improving network performance.

According to a second aspect, a communication method is provided, wherethe method includes:

sending, by a terminal device to a network device, a random accesspreamble;

receiving, by the terminal device, a random access response RAR sent bythe network device, where the RAR indicates a first resource; and

sending, by the terminal device, downlink channel quality indicationinformation to the network device, where the downlink channel qualityindication information is carried in a Message 3 that is sent by theterminal device by using the first resource, and the downlink channelquality indication information is used to indicate downlink channelquality.

Optionally, in an implementation of the second aspect, the sending, bythe terminal device, downlink channel quality indication information tothe network device includes:

sending, by the terminal device, the downlink channel quality indicationinformation to the network device based on configuration information,where the configuration information is carried in the RAR sent by thenetwork device, or the configuration information is carried in a systemmessage.

Optionally, in an implementation of the second aspect, the downlinkchannel quality indication information includes reference signalreceived quality RSRQ, or a quantity of NPDCCH repetition times duringRAR demodulation by the terminal device.

Specifically, when the network device receives the downlink channelquality indication information, the network device can properly select,based on the downlink channel quality, a maximum quantity of repetitiontimes of sending a Message 4. In addition, in an RRC connectionestablishment process, the network device properly configures a maximumvalue of a UE-specific search space USS of the terminal device based onthe downlink channel quality.

Therefore, in this embodiment of this application, the terminal devicereports the downlink channel quality, so that the network device canproperly determine the maximum quantity of repetition times of sendingthe Message 4 and/or the maximum value of the UE-specific search spaceUSS of the terminal device based on the downlink channel quality. Thisresolves an existing problem and avoids excessive power consumption ofthe terminal device and a system resource waste, thereby improvingnetwork performance.

According to a third aspect, a communication method is provided,including:

determining, by a terminal device, a current coverage level based onreference signal receiving performance; and

performing, by the terminal device, random access at the currentcoverage level.

Optionally, in an implementation of the third aspect, the determining,by a terminal device, a current coverage level based on reference signalreceiving performance includes:

determining, by the terminal device, the current coverage level based onthe reference signal receiving performance and reference signal receivedpower.

Optionally, in an implementation of the third aspect, the determining,by the terminal device, the current coverage level based on thereference signal receiving performance and reference signal receivedpower includes:

determining, by the terminal device, an initial coverage level based onthe reference signal received power; and

when the initial coverage level does not match the reference signalreceiving performance, determining, by the terminal device, a coveragelevel corresponding to the reference signal receiving performance as thecurrent coverage level.

Optionally, in an implementation of the third aspect, the performing, bythe terminal device, random access at the current coverage levelincludes:

sending, by the terminal device to a network device, a random accesspreamble, where transmit power of the preamble is determined by theterminal device based on target received power of the preamble and apath loss between the terminal device and the network device, and thetarget received power of the preamble is related to a current power rampstep and a current quantity of times of sending the preamble by theterminal device.

Optionally, in an implementation of the third aspect, the transmit powerof the preamble is determined by the terminal device according to thefollowing formula:

P _(NPRACH)=min{P _(CMAX) , P _(TARGET) +PL} [dBm], where

P_(NPRACH) represents the transmit power of the preamble,P_(CMAX)represents maximum transmit power of the terminal device, P_(TARGET)represents the target received power of the preamble, and PL representsthe path loss, where

P _(TARGET) =P _(P)+(M−1) P_(S), where

P_(P) represents initial target received power of the preamble, Mrepresents the current quantity of sending times, and P_(S) representsthe current power ramp step; or

P_(TARGET)=P_(P)+(M −1) P_(S)−10×log₁₀N_(r), where N_(r) is a quantityof repetition times of sending the preamble.

Therefore, in this embodiment of this application, the terminal devicemay determine the current coverage level based on the reference signalreceiving performance, so that the current coverage level can beflexibly and accurately determined, improving network performance.

According to a fourth aspect, a communication method is provided,including:

receiving, by a terminal device, indication information sent by anetwork device, where the indication information is used to indicate aquantity of repetition times of sending uplink information by theterminal device; and

when the terminal device determines that the quantity of repetitiontimes is greater than a second threshold, sending, by the terminaldevice, the uplink information by using maximum transmit power; or

when the terminal device determines that the quantity of repetitiontimes is less than or equal to the second threshold, sending, by theterminal device, the uplink information by using first power, where thefirst power is determined by the terminal device based on at least oneof a path loss, a path loss compensation factor, or transmissionbandwidth.

Optionally, in an implementation of the fourth aspect, the indicationinformation is carried in an uplink grant UL grant, and the uplinkinformation is uplink data; or the indication information is carried ina random access response RAR, and the uplink information is a Message 3.

Optionally, in an implementation of the third aspect, the secondthreshold is preset, the second threshold is indicated by the RAR, orthe second threshold is configured by using a system message.

Therefore, in this embodiment of this application, because the specifiedsecond threshold is greater than 2, even if a quantity of repetitiontimes configured by the network device for the Message 3 is greater than2, the terminal device may send the Message 3 by using, for example, thefirst power instead of the maximum power, provided that the quantity ofrepetition times is less than the second threshold, so as to reduce anoise floor of the network device and reduce impact on another terminaldevice, thereby improving network performance.

According to a fifth aspect, a communication method is provided,including:

sending, by a network device, a reference signal to a terminal device,so that the terminal device determines a current coverage level from atleast two coverage levels based on reference signal received power,where each of the at least two coverage levels is corresponding to apower ramp step; and

receiving, by the network device, a random access preamble, where thepreamble is sent by the terminal device in a power ramping manner basedon a current power ramp step corresponding to the current coveragelevel.

Therefore, in this embodiment of this application, during levelswitching, the terminal device still sends the preamble by using powerdetermined in a power ramping manner, and a prior-art manner of directlysending a preamble by using maximum power is abandoned. This can reduceimpact on another terminal device.

Optionally, in an implementation of the fifth aspect, the method furtherincludes:

sending, by the network device, indication information to the terminaldevice, where the indication information is used to indicate a quantityof repetition times of sending uplink information by the terminaldevice; and

receiving, by the network device, the uplink information, where when thequantity of repetition times is greater than a second threshold, theuplink information is sent by the terminal device by using maximumtransmit power; or

when the quantity of repetition times is less than or equal to thesecond threshold, the uplink information is sent by the terminal deviceby using first power, where the first power is determined by theterminal device based on at least one of a path loss, a path losscompensation factor, or transmission bandwidth.

Optionally, in an implementation of the fifth aspect, the indicationinformation is carried in an uplink grant UL grant, and the uplinkinformation is uplink data; or

the indication information is carried in a random access response RAR,and the uplink information is a Message 3.

Optionally, in an implementation of the fifth aspect, the secondthreshold is preset, the second threshold is indicated by the RAR, orthe second threshold is configured by using a system message.

Optionally, in an implementation of the fifth aspect, the method furtherincludes:

receiving, by the network device, downlink channel quality indicationinformation sent by the terminal device, where the downlink channelquality indication information is carried in a Message 3 that is sent bythe terminal device and that is received by the network device, and thedownlink channel quality indication information is used to indicatedownlink channel quality; and

determining, by the network device, a maximum quantity of repetitiontimes of sending a Message 4 and/or a maximum value of a USS of theterminal device based on the downlink channel quality.

Optionally, in an implementation of the fifth aspect, the downlinkchannel quality indication information is sent by the terminal devicebased on an indication of configuration information, where theconfiguration information is carried in an RAR sent by the networkdevice, or the configuration information is carried in a system message.

Optionally, in an implementation of the fifth aspect, the downlinkchannel quality indication information includes reference signalreceived quality RSRQ, or a quantity of NPDCCH repetition times duringRAR demodulation by the terminal device.

Therefore, in this embodiment of this application, the terminal devicereports the downlink channel quality, so that the network device canproperly determine the maximum quantity of repetition times of sendingthe Message 4 and/or the maximum value of the USS of the terminal devicebased on the downlink channel quality. This resolves an existing problemand avoids excessive power consumption of the terminal device and asystem resource waste, thereby improving network performance.

According to a sixth aspect, a communication method is provided,including:

receiving, by a network device, a random access preamble sent by aterminal device;

sending, by the network device, a random access response RAR to theterminal device, where the RAR indicates a first resource;

receiving, by the network device, downlink channel quality indicationinformation sent by the terminal device, where the downlink channelquality indication information is carried in a Message 3 that is sent bythe terminal device by using the first resource, and the downlinkchannel quality indication information is used to indicate downlinkchannel quality; and

determining, by the network device, a maximum quantity of repetitiontimes of sending a Message 4 and/or a maximum value of a USS of theterminal device based on the downlink channel quality.

Optionally, in an implementation of the sixth aspect, the downlinkchannel quality indication information is sent by the terminal devicebased on an indication of configuration information, where theconfiguration information is carried in the RAR sent by the networkdevice, or the configuration information is carried in a system message.

Optionally, in an implementation of the sixth aspect, the downlinkchannel quality indication information includes reference signalreceived quality RSRQ, or a quantity of NPDCCH repetition times duringRAR demodulation by the terminal device.

Therefore, in this embodiment of this application, the terminal devicereports the downlink channel quality, so that the network device canproperly determine the maximum quantity of repetition times of sendingthe Message 4 and/or the maximum value of the USS of the terminal devicebased on the downlink channel quality. This resolves an existing problemand avoids excessive power consumption of the terminal device and asystem resource waste, thereby improving network performance.

According to a seventh aspect, a communication method is provided,including: sending, by a network device, indication information to aterminal device, where the indication information is used to indicate aquantity of repetition times of sending uplink information by theterminal device; and

receiving, by the network device, the uplink information, where when thequantity of repetition times is greater than a second threshold, theuplink information is sent by the terminal device by using maximumtransmit power; or when the quantity of repetition times is less than orequal to the second threshold, the uplink information is sent by theterminal device by using first power, where the first power isdetermined by the terminal device based on at least one of a path loss,a path loss compensation factor, or transmission bandwidth.

Optionally, in an implementation of the seventh aspect, the indicationinformation is carried in an uplink grant UL grant, and the uplinkinformation is uplink data; or the indication information is carried ina random access response RAR, and the uplink information is a Message 3.

Optionally, in an implementation of the seventh aspect, the secondthreshold is preset, the second threshold is indicated by the RAR, orthe second threshold is configured by using a system message.

Therefore, in this embodiment of this application, because the specifiedsecond threshold is greater than 2, even if a quantity of repetitiontimes configured by the network device for the Message 3 is greater than2, the terminal device may send the Message 3 by using, for example, thefirst power instead of the maximum power, provided that the quantity ofrepetition times is less than the second threshold, so as to reduce anoise floor of the network device and reduce impact on another terminaldevice, thereby improving network performance.

According to an eighth aspect, a terminal device is provided, configuredto perform the method in any one of the first to the fourth aspects orthe possible implementations of the first to the fourth aspects.Specifically, the terminal device includes units configured to performthe foregoing method.

According to a ninth aspect, a network device is provided, configured toperform the method in any one of the fifth to the seventh aspects or thepossible implementations of the fifth to the seventh aspects.Specifically, the network device includes units configured to performthe foregoing method.

According to a tenth aspect, a computer-readable medium is provided. Thecomputer-readable medium stores a computer program, and when thecomputer program is executed by a computer, the method in any one of thefirst to the fourth aspects or the possible implementations of the firstto the fourth aspects is implemented.

According to an eleventh aspect, a computer-readable medium is provided.The computer-readable medium stores a computer program, and when thecomputer program is executed by a computer, the method in any one of thefifth to the seventh aspects or the possible implementations of thefifth to the seventh aspects is implemented.

According to a twelfth aspect, a computer program product is provided.When the computer program product is executed by a computer, the methodin any one of the first to the fourth aspects or the possibleimplementations of the first to the fourth aspects is implemented.

According to a thirteenth aspect, a computer program product isprovided. When the computer program product is executed by a computer,the method in any one of the fifth to the seventh aspects or thepossible implementations of the fifth to the seventh aspects isimplemented.

According to a fourteenth aspect, a processing apparatus is provided,including a processor and an interface, where the processor isconfigured to perform the method in any one of the first to the fourthaspects or the possible implementations of the first to the fourthaspects.

According to a fifteenth aspect, a processing apparatus is provided,including a processor and an interface, where the processor isconfigured to perform the method in any one of the fifth to the seventhaspects or the possible implementations of the fifth to the seventhaspects.

It should be understood that the processing apparatus in the fourteenthaspect or the fifteenth aspect may be a chip, and the processor may beimplemented by using hardware or software. When the processor isimplemented by using hardware, the processor may be a logic circuit, anintegrated circuit, or the like. When the processor is implemented byusing software, the processor may be a general purpose processor, and isimplemented by reading software code stored in a memory. The memory maybe integrated into the processor, or may be located outside theprocessor, and exist independently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a scenario to which an embodiment ofthis application can be applied;

FIG. 2 is a schematic flowchart of a communication method according toan embodiment of this application;

FIG. 3 is a schematic flowchart of a communication method according toanother embodiment of this application;

FIG. 4 is a schematic flowchart of a communication method according toanother embodiment of this application;

FIG. 5 is a schematic flowchart of data transmission according toanother embodiment of this application;

FIG. 6 is a schematic flowchart of a communication method according toanother embodiment of this application;

FIG. 7 is a schematic flowchart of a communication method according toanother embodiment of this application;

FIG. 8 is a schematic flowchart of a communication method according toanother embodiment of this application;

FIG. 9 is a schematic block diagram of a terminal device according to anembodiment of this application;

FIG. 10 is a schematic block diagram of a network device according to anembodiment of this application;

FIG. 11 is a schematic block diagram of a terminal device according toanother embodiment of this application; and

FIG. 12 is a schematic block diagram of a network device according toanother embodiment of this application.

DESCRIPTION OF EMBODIMENTS

The following details technical solutions of this application withreference to the accompanying drawings.

It should be understood that the technical solutions in the embodimentsof the present invention may be applied to NB-IoT communication. TheNB-IoT communication may be carried in various communications systems.For example, the embodiments of this application may be applied to: aglobal system for mobile communications (global system of mobilecommunication, GSM) system, a code division multiple access (codedivision multiple access, CDMA) system, a wideband code divisionmultiple access (wideband code division multiple access, WCDMA) system,a general packet radio service (general packet radio service, GPRS)system, a long term evolution (long term evolution, LTE) system, an LTEfrequency division duplex (frequency division duplex, FDD) system, anLTE time division duplex (time division duplex, TDD) system, a universalmobile telecommunications system (universal mobile telecommunicationsystem, UMTS), a wireless local area network (wireless local areanetwork, WLAN) system, a wireless fidelity (wireless fidelity, Wi-Fi)system, and a next-generation communications system, that is, a 5thgeneration (5th generation, 5G) communications system such as a newradio (new radio, NR) system.

In the embodiments of this application, a network device may be a basetransceiver station (base transceiver station, BTS) in global system formobile communications (global system of mobile communication, GSM) orcode division multiple access (code division multiple access, CDMA); ormay be a NodeB (nodeB, NB) in wideband code division multiple access(wideband code division multiple access, WCDMA); or may be an evolvedNodeB (evolutional node B, eNB/eNodeB) in long term evolution (long termevolution, LTE), a relay node, an access point, a vehicle-mounteddevice, a wearable device, or a network-side device in a future 5Gnetwork, for example, a transmission point (TRP or TP) in an NR system,a next-generation NodeB (gNB) in an NR system, or one antenna panel or agroup of antenna panels (including a plurality of antenna panels) of agNB in a 5G system. This is not particularly limited in the embodimentsof this application.

In the embodiments of this application, a terminal device may also bereferred to as user equipment (user equipment, UE), an access terminal,a subscriber unit, a subscriber station, a mobile station, a mobileconsole, a remote station, a remote terminal, a mobile device, a userterminal, a terminal, a wireless communications device, a user agent, ora user apparatus. The access terminal may be a cellular phone, acordless telephone set, a session initiation protocol (sessioninitiation protocol, SIP) phone, a wireless local loop (wireless localloop, WLL) station, a personal digital assistant (personal digitalassistant, PDA), a handheld device having a wireless communicationfunction, a computing device, another processing device connected to awireless modem, a vehicle-mounted device, a wearable device, an unmannedaerial vehicle device, or a terminal device in a future 5G network. Theterminal device may alternatively be an interne-of-things terminaldevice, such as a smart water meter, a smart electricity meter, aprinter, or a smart television set.

FIG. 1 is a schematic block diagram of a wireless communications system100 to which an embodiment of this application is applicable. Thewireless communications system 100 may include a network device 110 andat least one terminal device, such as terminal devices 120, 130, and140. The at least one terminal device may include any one of theterminal devices described above. For example, the terminal device 120is user equipment, the terminal device 130 is a vehicle-mounted device,and the terminal device 140 is a printer. The at least one terminaldevice may communicate with the network device 110 through a cellularnetwork. Different network devices corresponding to the at least oneterminal device may be located at different geographic locations, forexample, on a road, in a basement, and in a park. Therefore, channelconditions used by different terminal devices to communicate with thenetwork device are not totally the same.

To ensure communication reliability and reduce transmit power of thenetwork device, terminal devices in different channel conditions need tobe distinguished, to help the network device perform scheduling. In viewof this, a concept “coverage level” is introduced in an NB-IoT system.Channel transmission conditions of terminal devices at a same coveragelevel are similar. The network device may use a similar schedulingparameter for such users, and control signaling overheads occupied bythe users are also similar.

As described above, in the existing NB-IoT system, if a terminal devicefails in performing access at a coverage level 0, the terminal deviceswitches to a coverage level 1 for random access. According to anexisting protocol, the terminal device needs to send a preamble throughan NPRACH by using maximum power. In this case, the terminal device isstill at the coverage level 0 actually, and is relatively close to abase station. Therefore, if the preamble is sent through the NPRACH byusing the maximum power, a noise floor of a receiver of a network deviceis increased, affecting RACH access of a terminal device at anotherhigher coverage level. In view of this problem, an embodiment of thisapplication provides a communication method: At a coverage level 1 and acoverage level 2, the terminal device can also send, in a power rampingmanner, a random access preamble, and a prior-art solution of directlysending a preamble by using maximum power is abandoned. In this way,this embodiment of this application can resolve a problem that is causedby excessively high transmit power when the terminal device switchesfrom a coverage level 0 to the coverage level 1, thereby reducing impacton another terminal device.

For ease of understanding and description, by way of example but notlimitation, the following describes an execution process and actions ina communications system in a communication method in this application.

For ease of understanding the communication method in thisspecification, that a terminal performs complete service accessprocedure in this embodiment of this application is first described.

A terminal device may first detect a narrowband primary synchronizationsignal (narrowband primary synchronization signal, NPSS) and anarrowband secondary synchronization signal (narrowband secondarysynchronization signal, NSSS), to obtain cell ID information andcomplete downlink synchronization, such as frame synchronization orsymbol synchronization. Then, the terminal device obtains a systemmessage, where the system message may include a reference signalreceived power threshold used by the terminal device to determine acoverage level. Afterwards, the terminal device determines a currentcoverage level, and sends a preamble through an NPRACH by using aquantity of repetition times and a resource that are corresponding tothe current coverage level, to perform random access. After the randomaccess, the terminal device may request to perform uplink scheduling fordata transmission.

This embodiment of this application mainly describes improvements madein a random access procedure, as well as improvements made in a datatransmission process.

For ease of further understanding the solutions of this application, thefollowing first describes a random access procedure in an NB-IoT systemin this embodiment of this application briefly. Specifically, a randomaccess procedure 200 shown in FIG. 2 includes the following steps.

210. A terminal device receives a system message.

The system message may include various cell-level parameters, and mayfurther include a coverage level threshold. The system message furtherincludes indication information of an NPRACH resource corresponding toeach coverage level, and the like. For example, the NPRACH resource maybe a time domain resource, a frequency domain resource, or atime-frequency resource.

220. The terminal device sends a preamble by using an NPRACH resource.

For example, the terminal device may first determine a current coveragelevel, and then send the preamble on an NPRACH resource corresponding tothe coverage level.

230. A network device sends a random access response RAR to the terminaldevice by using an NPDCCH resource.

240. The terminal device sends a Message 3 to the network device byusing a narrowband physical uplink shared channel (narrowband physicaluplink shared channel, NPUSCH) resource.

250. The network device sends a Message 4 to the terminal device byusing a narrowband physical downlink shared channel (narrowband physicaluplink downlink channel, NPDSCH) resource.

So far, after the terminal device receives the Message 4, it indicates arandom access success, and the terminal device can send a datascheduling request or the like to the network device.

The foregoing only describes the random access procedure in thisembodiment of this application briefly. Specifically, for content ofeach message in each process, refer to descriptions in a relatedstandard. Details are not described in this embodiment of thisapplication.

Improvements to one or more of steps 210 to 250 or improvements to datatransmission after step 250 are made in the following embodiments ofthis application. The following specifically provides descriptionsseparately. It should be understood that improved steps are detailed inthe following embodiments, and details of steps similar to those in theprior art are properly omitted.

The following details a communication method in the embodiments of thisapplication with reference to the accompanying drawings.

It should be understood that, data transmitted between a network deviceand a terminal device in the communication method in the embodiments ofthis application may include but is not limited to the followingcontent: a system message, a broadcast message, control signaling,signaling on a control channel, and data on a data channel.

It should be noted that some names and English abbreviations in thisspecification are used to describe the embodiments of this applicationby using an NB-IoT system as an example. However, the embodiments ofthis application are not limited thereto. The names and Englishabbreviations may vary with network evolution. For specific evolution,refer to descriptions in a corresponding standard.

FIG. 3 is a schematic flowchart of a communication method according toan embodiment of this application. As shown in FIG. 3, the method 300includes the following steps.

310. A terminal device determines a current coverage level.

Specifically, the terminal device may determine the current coveragelevel from at least two coverage levels, and each of the at least twocoverage levels is corresponding to a power ramp step (power rampingstep).

It should be understood that the power ramp step indicates a powerincrease amplitude when the terminal device resends a preamble afterfailing in sending the preamble at the current coverage level. The powerramp step may also be referred to as a power increase step. Thisembodiment of this application is not limited thereto.

It should be understood that, in this embodiment of this application,after the terminal device sends a preamble, if no RAR is received, itindicates that the sending fails; or when the terminal device receivesan RAR but the RAR does not include the sent preamble, it also indicatesthat the sending fails.

In this embodiment of this application, at least two power ramp stepscorresponding to the at least two coverage levels may be not equal toeach other, or at least two power ramp steps corresponding to the atleast two coverage levels may be partially or all equal to each other.This is not limited in this embodiment of this application.

It should be understood that the at least two coverage levels in thisembodiment of this application may mean two, three, four, five, or morecoverage levels. Three coverage levels, that is, coverage levels 0, 1,and 2, are mainly used as an example for description in thisspecification. However, this is not limited in this embodiment of thisapplication. In actual application, a quantity of coverage levels may bedetermined depending on an actual situation.

For example, a network device sends a reference signal to the terminaldevice, and the terminal device may determine the current coverage levelfrom the at least two coverage levels based on reference signal receivedpower (RSRP).

Specifically, the terminal device may obtain a threshold of thereference signal received power based on a system message, or thethreshold of the reference signal received power is preset. This is notlimited in this embodiment of this application. For example, thethreshold of the reference signal received power may include twothresholds: a power threshold 1 and a power threshold 2, where the powerthreshold 1 is less than the power threshold 2. The terminal devicecompares an RSRP value with the two power thresholds, to determine thecurrent coverage level. For example, when the RSRP value is less thanthe power threshold 1, it is determined that the current coverage levelis a coverage level 2; when the RSRP value is greater than the powerthreshold 2, it is determined that the current coverage level is acoverage level 0; or when the RSRP value is between the power threshold1 and the power threshold 2, it is determined that the current coveragelevel is a coverage level 1.

Optionally, the terminal device may alternatively determine the currentcoverage level from the at least two coverage levels based on referencesignal receiving performance.

The reference signal receiving performance may include a signal-to-noiseratio (Signal Noise Ratio, SNR) of a reference signal or referencesignal received quality (reference signal received quality, RSRP). Forexample, the terminal device may compare current receiving performancewith a receiving performance threshold, to determine the currentcoverage level. It should be understood that, when the reference signalreceiving performance is an SNR, the receiving performance threshold isan SNR threshold; or when the reference signal receiving performance isRSRP, the receiving performance threshold is an RSRP threshold. Thereceiving performance threshold may be carried in a system message, ormay be preset by a system. This embodiment of this application is notlimited thereto. For example, the reference signal receiving performancethreshold may include two thresholds: a performance threshold 1 and aperformance threshold 2, where the performance threshold 1 is less thanthe performance threshold 2. The terminal device compares a value of thereference signal receiving performance with the two performancethresholds, to determine the current coverage level. For example, whenthe value of the receiving performance is less than the performancethreshold 1, it is determined that the current coverage level is acoverage level 2; when the value of the receiving performance is greaterthan the performance threshold 2, it is determined that the currentcoverage level is a coverage level 0; or when the value of the receivingperformance is between the performance threshold 1 and the performancethreshold 2, it is determined that the current coverage level is acoverage level 1.

Optionally, the terminal device may alternatively determine the coveragelevel based on reference signal received power and the reference signalreceiving performance.

Specifically, the terminal device determines an initial coverage levelbased on the reference signal received power; and

when the initial coverage level does not match the reference signalreceiving performance, the terminal device determines a coverage levelcorresponding to the reference signal receiving performance as thecurrent coverage level.

It should be understood that each coverage level in this embodiment ofthis application may be corresponding to a reference signal receivingperformance range. The terminal device may first determine an initialcoverage level based on the reference signal received power. When theinitial coverage level matches the reference signal receivingperformance, that is, when the reference signal receiving performancefalls within a reference signal receiving performance rangecorresponding to the initial coverage level, the terminal devicedetermines the initial coverage level as the current coverage level.When the initial coverage level does not match the reference signalreceiving performance, that is, when the reference signal receivingperformance is beyond the reference signal receiving performance rangecorresponding to the initial coverage level, the terminal devicedetermines the coverage level corresponding to the reference signalreceiving performance as the current coverage level.

For example, if RSRP measured by the terminal device at the beginning isat a coverage level N, but an SNR obtained through measurement isundesirable and is lower than an SNR at the current coverage level, theterminal device directly sends a preamble at a coverage level N+1 or acoverage level N+2 corresponding to the reference signal receivingperformance.

For example, when the reference signal received power is correspondingto the coverage level N, and the reference signal receiving performanceis corresponding to the coverage level N+1, the terminal devicedetermines that the current coverage level is the coverage level N+1; or

when the reference signal received power is corresponding to thecoverage level N, and the reference signal receiving performance iscorresponding to the coverage level N+2, the terminal device determinesthat the current coverage level is the coverage level N+2.

Specifically, in the prior art, a terminal device determines a coveragelevel based only on reference signal received power. However, there is acase: Reference signal receiving performance may be relatively pooralthough the reference signal received power is relatively high. If thecoverage level is determined based only on the reference signal receivedpower, a current channel status cannot be well reflected. Therefore, inthis embodiment of this application, the terminal device may determinethe current coverage level based on the reference signal receivingperformance, so that the current coverage level can be flexibly andaccurately determined, improving network performance.

It should be understood that, in this embodiment of this application, anext coverage level of the coverage level 0 is the coverage level 1, anext coverage level of the coverage level 1 is the coverage level 2, andso on. The coverage level 0 indicates best channel quality. As acoverage level increases, channel quality gradually deteriorates.

It should be understood that, in this embodiment of this application,each coverage level may be corresponding to a quantity of repetitiontimes. The quantity of repetition times indicates a quantity ofrepetition times of sending a preamble by the terminal device. In otherwords, the quantity of repetition times indicates a quantity of times apreamble is repeated when the terminal device sends the preamble. Forexample, assuming that the preamble is A, when a quantity of repetitiontimes corresponding to the current coverage level is 5, each time theterminal device sends the preamble at the current coverage level, theterminal device sends the following content: AAAAA.

320. The terminal device sends a preamble.

For example, the terminal device sends, to the network device in a powerramping manner based on a current power ramp step corresponding to thecurrent coverage level, a random access preamble.

Therefore, in this embodiment of this application, the terminal devicesends the preamble at the current level by using power determined in apower ramping manner, and a prior-art manner of directly sending apreamble by using maximum power is abandoned. This can reduce impact onanother terminal device.

Specifically, when failing in sending the preamble last time, theterminal device increases transmit power of the preamble by the currentpower ramp step corresponding to the current coverage level, to obtainnew power; and resends the preamble by using the new power.

It should be understood that sending the preamble by the terminal devicein a power ramping manner may also be referred to as sending thepreamble by the terminal device in a power increasing manner. Thisembodiment of this application is not limited thereto.

For example, when the terminal device sends the preamble at the currentcoverage level for the first time, the terminal device sends thepreamble by using first-time power.

It should be understood that, in this embodiment of this application,sending a preamble once indicates sending the preamble based on aquantity of repetition times corresponding to the current coveragelevel.

When the sending for the first time fails, the terminal device resendsthe preamble after increasing the first-time power by a power ramp step.Other cases are by analogy with the foregoing. Optionally, in actualapplication, in step 320, the terminal device may determine, based ontarget received power of the preamble and a path loss between theterminal device and the network device, the transmit power of thepreamble, where the target received power of the preamble is related tothe current power ramp step and a current quantity of times of sendingthe preamble by the terminal device.

It should be understood that the current quantity of sending times mayindicate a quantity of times of sending the preamble by the terminaldevice. For example, if a current preamble to be sent is resent afterthe terminal device fails in sending the preamble Z times, the currentquantity of sending times is equal to Z+1, indicating that the terminaldevice is sending the preamble for a (Z+1)^(th) time.

Optionally, the transmit power of the preamble is determined by theterminal device according to the following formula:

P _(NPRACH)=min{P_(CMAX) , P _(TARGET) PL} [dBm], where

P_(NPRACH) represents the transmit power of the preamble,P_(CMAX)represents maximum transmit power of the terminal device, P_(TARGET)represents the target received power of the preamble, and PL representsthe path loss, where

P _(TARGET) =P _(P)+(M−1) Ps, where

P_(P) represents initial target received power of the preamble, Mrepresents the current quantity of sending times, and Ps represents thecurrent power ramp step; or

P_(TARGET)=P_(P)+(M −1) P_(s)−10 ×log₁₀N_(r), where N_(r) is a quantityof repetition times of sending the preamble.

It should be understood that, in this embodiment of thisapplication,P_(CMAX) is a parameter P_(CMAX, c) ^((i)) in a protocol andindicates maximum transmit power of the terminal device in a servingcell c in an NB-IoT uplink slot i, P_(TARGET) is a parameterNARROWBAND_PREAMBLE_RECEIVED_TARGET_POWER in the protocol or P_(TARGET)is a parameter PREAMBLE_RECEIVED_TARGET_POWER in the protocol, PL is aparameter PL_(c) in the protocol and indicates a downlink path loss,P_(P) is a parameter preamblelnitialReceivedTargetPower in the protocol,M is a parameter PREAMBLE_TRANSMISSION_COUNTER in the protocol, andN_(r) is a parameter numRepetitionPerPreambleAttempt in the protocol.

It should be understood that the foregoing formula is only a specificform of determining the transmit power, and variation may be performedappropriately based on the foregoing formula. This embodiment of thisapplication is not limited thereto.

Optionally, in another embodiment, when a quantity of times of sendingthe preamble by the terminal device at the current coverage level isgreater than a first threshold, the terminal device sends the preambleto the network device at a next coverage level of the current coveragelevel, where

the first threshold is less than a maximum quantity of times oftransmitting a preamble (maximum number of preamble transmissionattempts per enhanced coverage level, maxNumPreambleAttemptCE) at thecurrent coverage level defined in a standard.

Specifically, if the terminal device still fails after attempting for aquantity of times at the coverage level N, where the quantity of timesis equal to the first threshold, the terminal device directly sends thepreamble at the coverage level N+1.

Specifically, in an existing solution, the terminal device switches to anext coverage level to send the preamble, only after the quantity oftimes of sending the preamble at the current coverage level is greaterthan the maximum quantity of times of transmitting a preamble at thecurrent coverage level.

In contrast, in this embodiment of this application, when the quantityof times of sending the preamble at the current coverage level isgreater than the first threshold, coverage level switching may beperformed. Because the first threshold is less than the maximum quantityof times of transmitting a preamble, when current channel quality isrelatively poor, a quantity of unnecessary failures at the currentcoverage level can be reduced. This reduces a resource waste andimproves network performance.

It should be understood that, in this embodiment of this application,after switching to the next coverage level is performed, the preamblemay be sent by using a resource corresponding to the next coveragelevel, a quantity of repetition times corresponding to the next coveragelevel, or power corresponding to the next coverage level.

For example, after switching from a coverage level N to a coverage levelN+1, the terminal device may send the preamble by using a resource andpower that are corresponding to the coverage level N+1.

Optionally, after switching to the coverage level N+1, the terminaldevice may send the preamble by using maximum power.

Optionally, after switching to the next level, the terminal device mayalternatively send the preamble at the next level in a power rampingmanner.

Specifically, the manner of switching to the coverage level N+1 andsending the preamble in a power ramping manner may be similar to sendingthe preamble at the coverage level N in a ramping manner, and adifference lies in that a quantity of repetition times corresponding tothe coverage level N+1 is greater than a quantity of repetition timescorresponding to the coverage level N. To avoid repetition, details arenot described herein again.

Optionally, in another embodiment, after the terminal device switchesfrom the current coverage level to the next level, the terminal devicesends the preamble in a power ramping manner by using a quantity ofrepetition times corresponding to the next coverage level and thecurrent power ramp step corresponding to the current coverage level.

Specifically, when the terminal device has performed coverage levelswitching for random access, for example, switched from a coverage levelN to a coverage level N+1 (N=0 or N=1), the terminal device sends thepreamble still in a previous power control manner (that is, a powercontrol manner at the coverage level N), but sends the preamble by usinga quantity of repetition times at the coverage level N+1.

Therefore, in this embodiment of this application, during levelswitching, the terminal device still sends the preamble by using powerdetermined in a power ramping manner, and a prior-art manner of directlysending a preamble by using maximum power is abandoned. This can reduceimpact on another terminal device. In addition, after the levelswitching, although the transmit power is determined in a previous powercontrol manner, the preamble is sent based on the quantity of repetitiontimes corresponding to the next coverage level, so that a quantity ofrepetition times of the preamble during each transmission can beincreased, thereby improving an access success probability.

After step 320, the terminal device and the network device may perform asubsequent random access procedure in the existing manner.

Optionally, in another embodiment, as shown in FIG. 4, after step 320, amethod 400 in this embodiment of this application may further includethe following steps.

330. The terminal device receives indication information sent by thenetwork device.

Specifically, the indication information is used to indicate a quantityof repetition times of sending uplink information by the terminaldevice. The quantity of repetition times of sending the uplinkinformation may be a quantity of times the uplink information isrepeated when the terminal device sends the uplink information eachtime. To be specific, content sent each time is repetition of the uplinkinformation and is repeated for N times.

It should be understood that the network device may add the indicationinformation to an RAR in the random access procedure. Correspondingly,the uplink information is a Message 3.

Alternatively, the network device may add the indication information toan uplink grant (uplink grant, UL grant) obtained after random access iscompleted. Correspondingly, the uplink information may be uplink data.

340. The terminal device sends uplink information.

Specifically, when the terminal device determines that the quantity ofrepetition times is greater than a second threshold, the terminal devicesends the uplink information by using maximum transmit power; or

when the terminal device determines that the quantity of repetitiontimes is less than or equal to the second threshold, the terminal devicesends the uplink information by using first power, where the first poweris determined by the terminal device based on at least one of a pathloss, a path loss compensation factor, or transmission bandwidth.

Corresponding to step 330, the uplink information may be a Message 3 ormay be uplink data.

It should be understood that, in this embodiment of this application,the second threshold may be preset, may be indicated by the RAR, may beconfigured by using a system message, or may be indicated by an uplinkgrant message. This embodiment of this application is not limitedthereto.

It should be understood that the second threshold in this embodiment ofthis application may be an integer greater than 2.

Specifically, when the terminal device switches from a coverage level Nto a coverage level N+1 to send the preamble, after receiving an RAR,the terminal device may send a Message 3 based on an indication of theRAR. Because the network device has received the preamble on a resourcecorresponding to the coverage level N+1, the network device considersthat the terminal device is at the coverage level N+1 at this time, anda configured quantity of repetition times of the Message 3 may berelatively large and is, for example, greater than 2. In this case,according to stipulations in an existing standard, when the quantity ofrepetition times is greater than 2, the terminal device sends theMessage 3 by using maximum power. However, the terminal device may berelatively close to the network device, and if the Message 3 is sent byusing the maximum power, a noise floor of the network device increases,causing interference to another terminal device and affecting networkperformance. In contrast, in this embodiment of this application,because the specified second threshold is greater than 2, even if aquantity of repetition times configured by the network device for theMessage 3 is greater than 2, the terminal device may send the Message 3by using, for example, the first power instead of the maximum power,provided that the quantity of repetition times is less than the secondthreshold, so as to reduce a noise floor of the network device andreduce impact on another terminal device, thereby improving networkperformance.

For a method for determining the first power, refer to a method ofdetermining, when a quantity of repetition times of the Message 3 in anexisting standard is 1, power for sending the Message 3. Details are notdescribed herein.

Alternatively, in another embodiment, as shown in FIG. 5, after step320, a method 500 in this embodiment of this application may furtherinclude the following steps.

350. The terminal device receives an RAR sent by the network device.

Optionally, the RAR message may include configuration information, wherethe configuration information indicates downlink channel qualityindication information sent by the terminal device to the networkdevice, and the downlink channel quality indication information is usedto indicate downlink channel quality.

Optionally, in another embodiment, the configuration information may notbe carried in the RAR, for example, may be carried in a system message.Alternatively, it is preconfigured in a system for the terminal deviceto feed back the downlink channel quality indication information.

360. The terminal device sends a Message 3 to the network device.

The Message 3 carries the downlink channel quality indicationinformation.

Correspondingly, the network device receives the Message 3, and obtainsthe downlink channel quality indication information. Then, the networkdevice may determine a maximum quantity of repetition times of sending aMessage 4 and/or a maximum (Rmax) value of a USS of the terminal devicebased on the downlink channel quality. The maximum value of the USSindicates a maximum quantity of repetition times of an NPDCCH in theUE-specific search space of the terminal device.

The downlink channel quality indication information may includereference signal received quality (RSRQ), or a quantity of NPDCCHrepetition times during RAR demodulation by the terminal device.

Specifically, when the network device receives the downlink channelquality indication information, the network device can properly select,based on the downlink channel quality, the maximum quantity ofrepetition times of sending the Message 4. In addition, in an RRCconnection establishment process, the network device properly configuresthe maximum value of the USS based on the downlink channel quality.

Specifically, currently in NB-IoT, a specific coverage level isdetermined after the terminal device compares a downlink RSRPmeasurement value with an RSRP threshold preconfigured by the networkdevice. The RSRP threshold is set in consideration of ensuring, as muchas possible, receiving performance of a preamble on an uplink PRACH bythe network device. However, in actual network deployment, there is adifference between an uplink receiving interference level of the networkdevice and an interference level of a downlink terminal. In addition,because specific locations of terminals having a same RSRP aredifferent, there may also be a great difference between downlinkreceiving SNRs of the terminals. Therefore, the network device, that is,a base station, usually set, based on receiving performance of theuplink PRACH, the RSRP threshold used for determining a coverage level.Although the coverage level selected based on the RSRP thresholdreflects an uplink receiving status relatively accurately, it is quitedifficult to reflect a downlink SNR of the terminal. In this case, thenetwork device, that is, the base station, actually cannot accuratelylearn a downlink coverage status of the terminal, and can only configurea relatively conservative maximum quantity of repetition times of anNPDCCH search space or relatively conservatively schedule downlink data.Consequently, the specified quantity of repetition times of the searchspace is excessively large, or a quantity of repetition times of thedownlink data is relatively large. This results in relatively high powerconsumption of the terminal and a system resource waste, therebyaffecting network performance.

In contrast, in this embodiment of this application, the terminal devicereports the downlink channel quality, so that the network device canproperly determine the maximum quantity of repetition times of sendingthe Message 4 and/or the maximum value of the USS of the terminal devicebased on the downlink channel quality. This resolves an existing problemand avoids excessive power consumption of the terminal device and asystem resource waste, thereby improving network performance.

The foregoing describes the communication method performed by theterminal device in a power ramping manner with reference to FIG. 3 toFIG. 5.

FIG. 6 is a schematic flowchart of a communication method according toan embodiment of this application. In the method in FIG. 6, a solutionof reporting downlink channel quality by a terminal device can be addedbased on the existing solution in FIG. 2, so that a network deviceproperly performs downlink transmission. Specifically, the method 600shown in FIG. 6 includes the following steps.

610. The terminal device sends a preamble to the network device.

Specifically, the terminal device may send the preamble in an existingmanner or in the manner in step 320. To avoid repetition, details arenot described herein again.

620. The terminal device receives an RAR sent by the network device.

Optionally, step 620 is corresponding to step 350. To avoid repetition,details are not described herein again.

630. The terminal device sends a Message 3 to the network device.

Optionally, step 630 is corresponding to step 360. To avoid repetition,details are not described herein again.

Therefore, in this embodiment of this application, the terminal devicereports downlink channel quality, so that the network device canproperly determine a maximum quantity of repetition times of sending aMessage 4 and/or a maximum value of a USS of the terminal device basedon the downlink channel quality. This resolves an existing problem andavoids excessive power consumption of the terminal device and a systemresource waste, thereby improving network performance.

FIG. 7 is a schematic flowchart of a communication method according toan embodiment of this application. In the method in FIG. 7, a solutionof determining a current coverage level can be improved based on anexisting solution. Specifically, the method 700 shown in FIG. 7 includesthe following steps.

710. A terminal device determines a current coverage level.

Specifically, the terminal device determines the current coverage levelbased on reference signal receiving performance.

Specifically, optionally, the terminal device may determine the currentcoverage level from at least two coverage levels based on the referencesignal receiving performance.

The reference signal receiving performance may include a signal-to-noiseratio (SNR) of a reference signal or reference signal received quality.For example, the terminal device may compare current receivingperformance with a receiving performance threshold, to determine thecurrent coverage level. The receiving performance threshold may becarried in a system message, or may be preset by a system. Thisembodiment of this application is not limited thereto. For example, thereference signal receiving performance threshold may include twothresholds: a performance threshold 1 and a performance threshold 2,where the performance threshold 1 is less than the performance threshold2. The terminal device compares a value of the reference signalreceiving performance with the two performance thresholds, to determinethe current coverage level. For example, when the value of the receivingperformance is less than the performance threshold 1, it is determinedthat the current coverage level is a coverage level 2; when the value ofthe receiving performance is greater than the performance threshold 2,it is determined that the current coverage level is a coverage level 0;or when the value of the receiving performance is between theperformance threshold 1 and the performance threshold 2, it isdetermined that the current coverage level is a coverage level 1.

Optionally, the terminal device may alternatively determine the coveragelevel based on reference signal received power and the reference signalreceiving performance.

Specifically, the terminal device determines an initial coverage levelbased on the reference signal received power; and when the initialcoverage level does not match the reference signal receivingperformance, the terminal device determines a coverage levelcorresponding to the reference signal receiving performance as thecurrent coverage level.

It should be understood that each coverage level in this embodiment ofthis application may be corresponding to a reference signal receivingperformance range. The terminal device may first determine an initialcoverage level based on the reference signal received power. When theinitial coverage level matches the reference signal receivingperformance, that is, when the reference signal receiving performancefalls within a reference signal receiving performance rangecorresponding to the initial coverage level, the terminal devicedetermines the initial coverage level as the current coverage level.When the initial coverage level does not match the reference signalreceiving performance, that is, when the reference signal receivingperformance is beyond the reference signal receiving performance rangecorresponding to the initial coverage level, the terminal devicedetermines the coverage level corresponding to the reference signalreceiving performance as the current coverage level.

For example, if RSRP measured by the terminal device at the beginning isat a coverage level N, but an SNR obtained through measurement isundesirable and is lower than an SNR at the current coverage level, theterminal device directly sends a preamble at a coverage level N+1 or acoverage level N+2 corresponding to the reference signal receivingperformance.

For example, when the reference signal received power is correspondingto the coverage level N, and the reference signal receiving performanceis corresponding to the coverage level N+1, the terminal devicedetermines that the current coverage level is the coverage level N+1; or

when the reference signal received power is corresponding to thecoverage level N, and the reference signal receiving performance iscorresponding to the coverage level N+2, the terminal device determinesthat the current coverage level is the coverage level N+2.

It should be understood that, in this embodiment of this application, anext coverage level of the coverage level 0 is the coverage level 1, anext coverage level of the coverage level 1 is the coverage level 2, andso on. The coverage level 0 indicates best channel quality. As acoverage level increases, channel quality gradually deteriorates.

Specifically, in the prior art, a coverage level is determined basedonly on reference signal received power. In this case, reference signalreceiving performance may be relatively poor although the referencesignal received power is relatively high. If the coverage level isdetermined based only on the reference signal received power, a currentchannel status of the terminal device cannot be well reflected.Therefore, in this embodiment of this application, the terminal devicemay determine the current coverage level based on the reference signalreceiving performance, so that the current coverage level can beflexibly and accurately determined, improving network performance.

720. The terminal device sends a preamble.

Optionally, step 720 is corresponding to step 320. To avoid repetition,details are not described herein again.

Therefore, in this embodiment of this application, the terminal devicemay determine the current coverage level based on the reference signalreceiving performance, so that the current coverage level can beflexibly and accurately determined, improving network performance.

FIG. 8 is a schematic flowchart of a communication method according toan embodiment of this application. In the method in FIG. 8, a solutionof sending uplink information can be improved based on an existingsolution. Specifically, the method 800 shown in FIG. 8 includes thefollowing steps.

810. A terminal device receives indication information sent by a networkdevice.

Optionally, step 810 is corresponding to step 330. To avoid repetition,details are not described herein again.

820. The terminal device sends uplink information.

Therefore, in this embodiment of this application, because a specifiedsecond threshold is greater than 2, even if a quantity of repetitiontimes configured by the network device for a Message 3 is greater than2, the terminal device may send the Message 3 by using, for example,first power instead of maximum power, provided that the quantity ofrepetition times is less than the second threshold, so as to effectivelyreduce a noise floor of the network device and reduce impact on anotherterminal device, thereby improving network performance.

It should be noted that, the communication method in each of theforegoing embodiments may further include: when the terminal devicedetects that a coverage level corresponding to downlink channel qualitydoes not match a current coverage level, re-initiating, by the terminaldevice, a random access procedure at the coverage level corresponding tothe downlink channel quality. Specifically, after the terminal devicecompletes a random access procedure, that is, when the terminal deviceperforms data transmission with the network device, if the terminaldevice detects that the coverage level corresponding to the downlinkchannel quality does not match the current coverage level, the terminaldevice re-initiates the random access procedure based on the coveragelevel corresponding to the downlink channel quality, and then performsdata transmission after the re-initiated random access procedure iscompleted.

It should be understood that, for the specific re-initiated randomaccess procedure, reference may be made to the descriptions of theforegoing embodiments. Details are not described herein again.

For example, when downlink channel quality deteriorates so that thedownlink channel quality does not match a coverage level, ifcommunication is performed still based on a parameter corresponding tothe original coverage level, it is possible that the terminal devicecannot obtain downlink data, thereby affecting network performance. Incontrast, in this embodiment of this application, in such a case, randomaccess is re-initiated, so that the downlink channel quality matches thecoverage level. This resolves the foregoing problem and can improvenetwork performance.

It should be noted that, in each of the foregoing embodiments, when aquantity of times of failing in sending a preamble by the terminaldevice at the current coverage level is greater than a first thresholdor a maximum quantity of times of transmitting a preamble at the currentcoverage level, the terminal device needs to switch to a next coveragelevel to send the preamble. In a case of coverage level switching, theterminal device may further send switching indication information byusing the Message 3, where the switching indication information is usedto indicate whether the terminal device has performed coverage levelswitching. For example, the switching indication information is 1 bit inlength; and when the indication information is set to 0, it indicatesthat no coverage level switching has been performed; or when theindication information is set to 1, it indicates that the terminaldevice has performed coverage level switching. Alternatively, when theswitching indication information is set to 1, it indicates that theterminal has not performed coverage level switching; or when theswitching indication information is set to 0, it indicates that theterminal device has performed coverage level switching. In this way,after obtaining the Message 3, the network device may determine, basedon a value of the switching indication information, whether the terminaldevice has performed coverage level switching. When the terminal devicehas performed coverage level switching (for example, the terminal devicehas switched from a coverage level 0 to a coverage level 1), althoughthe terminal device sends the preamble at the coverage level 1, becausethe terminal device may be relatively close to the network device andthe downlink channel quality may be desirable, the network device maynot need to configure, based on the coverage level 1, a quantity ofrepetition times of sending a Message 4 and a maximum value of a USS.The network device can flexibly select a maximum quantity of repetitiontimes of sending the Message 4, and in an RRC connection establishmentprocess, the network device can properly configure the maximum value ofthe USS. For example, when the indication information indicates that theterminal device has performed coverage level switching, a quantity ofrepetition times of actually sending a Message 4 by the network devicemay be less than the quantity of repetition times of the Message 4corresponding to the coverage level 1, and a maximum value of the USSconfigured by the network device is less than the maximum value of theUSS corresponding to the coverage level 1. In this way, excessiveconsumption of the terminal device and a system resource waste can beavoided.

Therefore, in this embodiment of this application, the terminal devicereports the switching indication information, so that the network devicecan properly determine the maximum quantity of repetition times ofsending the Message 4 and/or the maximum value of the USS of theterminal device based on the switching indication information. Thisavoids excessive power consumption of the terminal device and a systemresource waste, thereby improving network performance.

It should be noted that each of the foregoing embodiments of thisapplication may be targeted for each release (release) of the 3rdGeneration Partnership Project (3rd generation partnership project,3GPP). In other words, a terminal device in each release (such as arelease 13, a release 14, or a release 15) of the 3GPP may performcommunication according to the foregoing embodiments.

Optionally, each of the foregoing embodiments may be targeted for aterminal device only in a new release (for example, the release 15). Forexample, the network device may send a system message in a presetmanner, so that only a terminal device in the release 15 can correctlydecode a coverage level threshold in the system message, and a terminaldevice in an old release (such as the release 13 or the release 14)cannot obtain the coverage level threshold. The terminal device in theold release can receive only a coverage level threshold in a systemmessage in the old release. During configuration of a quantity ofcoverage levels, a quantity of old-release coverage levels and aquantity of new-release coverage levels may be separately configured. Inthis case, the terminal device in the new release may perform randomaccess in a manner according to each of the foregoing embodiments inthis specification, whereas the terminal device in the old release maybe separately configured to have no coverage level threshold. Therefore,it is considered that all terminal devices in the old release have onlyone coverage level, that is, a coverage level 0, and all the terminaldevices in the old release perform random access at the existingcoverage level 0 in a power ramping manner. In such a manner, the methodin this embodiment of this application is compatible with a terminaldevice in the old release (such as the release 13 or the release 14). Inother words, this embodiment of this application is compatible withstipulations in an existing protocol, so that all terminal devices inthe old release perform random access in a power ramping mannercorresponding to the coverage level 0 in the existing protocol. Thisavoids a problem of an increase in a noise floor of a receiver of thenetwork device that is caused by coverage level switching by theterminal device in the old release. In addition, the terminal device inthe new release can perform coverage level switching, so that theproblem of the increase in the noise floor of the receiver of thenetwork device is resolved by using the method in this embodiment of thepresent invention.

It should be noted that, the examples in the foregoing embodiments aremerely intended to help a person skilled in the art understand theembodiments of this application, but not to limit the embodiments ofthis application to specific values or specific scenarios shown in theexamples. Apparently, a person skilled in the art can make variousequivalent modifications or changes to the examples provided above. Forexample, each of the foregoing embodiments of this application may becombined or embedded. The foregoing modifications or changes also fallwithin the scope of the embodiments of this application.

The foregoing details the communication methods according to theembodiments of this application with reference to FIG. 1 to FIG. 8, andthe following details devices according to the embodiments of thisapplication with reference to FIG. 9 to FIG. 12.

FIG. 9 is a schematic block diagram of a terminal device 900 accordingto an embodiment of this application. Specifically, as shown in FIG. 9,the terminal device 900 includes a processing unit 910 and a transceiverunit 920.

Specifically, the processing unit is configured to determine a currentcoverage level from at least two coverage levels based on referencesignal received power, where each of the at least two coverage levels iscorresponding to a power ramp step; and the transceiver unit isconfigured to send, to a network device in a power ramping manner basedon a current power ramp step corresponding to the current coveragelevel, a random access preamble.

Therefore, in this embodiment of this application, the terminal devicesends the preamble at the current level by using power determined in apower ramping manner, and a prior-art manner of directly sending apreamble by using maximum power is abandoned. This can reduce impact onanother terminal device.

Optionally, in another embodiment, the transceiver unit is specificallyconfigured to: when failing in sending the preamble last time, increasetransmit power of the preamble by the current power ramp step, to obtainnew power; and resend the preamble by using the new power.

Optionally, in another embodiment, the transceiver unit is furtherconfigured to: when a quantity of times of sending the preamble at thecurrent coverage level is greater than a first threshold, send thepreamble to the network device at a next coverage level of the currentcoverage level, where

the first threshold is less than a maximum quantity of times oftransmitting a preamble at the current coverage level.

Optionally, in another embodiment, the transceiver unit is specificallyconfigured to send the preamble in a power ramping manner by using aquantity of repetition times corresponding to the next coverage leveland the current power ramp step corresponding to the current coveragelevel.

The processing unit is specifically configured to determine the currentcoverage level from the at least two coverage levels based on referencesignal receiving performance.

Optionally, in another embodiment, the processing unit is specificallyconfigured to determine the current coverage level from the at least twocoverage levels based on reference signal received power and thereference signal receiving performance.

Optionally, in another embodiment, the processing unit is specificallyconfigured to: determine an initial coverage level based on thereference signal received power; and when the initial coverage leveldoes not match the reference signal receiving performance, determine acoverage level corresponding to the reference signal receivingperformance as the current coverage level.

Optionally, in another embodiment, the transceiver unit is furtherconfigured to: receive indication information sent by the networkdevice, where the indication information is used to indicate a quantityof repetition times of sending uplink information by the terminaldevice; and

when it is determined that the quantity of repetition times is greaterthan a second threshold, send the uplink information by using maximumtransmit power; or

when it is determined that the quantity of repetition times is less thanor equal to the second threshold, send the uplink information by usingfirst power, where the first power is determined by the terminal devicebased on at least one of a path loss, a path loss compensation factor,or transmission bandwidth.

Optionally, in another embodiment, the indication information is carriedin an uplink grant UL grant, and the uplink information is uplink data;or

the indication information is carried in a random access response RAR,and the uplink information is a Message 3.

Optionally, in another embodiment, the second threshold is preset, thesecond threshold is indicated by the RAR, or the second threshold isconfigured by using a system message.

Optionally, in another embodiment, the transmit power of the preamble isdetermined based on target received power of the preamble and a pathloss between the terminal device and the network device, and the targetreceived power of the preamble is related to the power ramp step and acurrent quantity of times of sending the preamble.

Optionally, in another embodiment, the transmit power of the preamble isdetermined by the transceiver unit according to the following formula:

P _(NPRACH)=min{P _(CMAX) , P _(TARGET) +PL} [dBm], where

P_(NPRACH) represents the transmit power of the preamble,P_(CMAX)represents the maximum transmit power of the terminal device, P_(TARGET)represents the target received power of the preamble, and PL representsthe path loss, where

P _(TARGET) =P _(P)+(M−1) P _(S), where

P_(p) represents initial target received power of the preamble, Mrepresents the current quantity of sending times, and P_(s) representsthe current power ramp step; or

P_(TARGET) =P _(P)+(M−1) P_(S)−10×log₁₀N_(r), where N_(r) is a quantityof repetition times of sending the preamble.

Optionally, in another embodiment, the transceiver unit is furtherconfigured to: when the terminal device detects that a coverage levelcorresponding to downlink channel quality does not match the currentcoverage level, re-initiate a random access procedure at the coveragelevel corresponding to the downlink channel quality. This process may beperformed after a random access procedure is completed.

Optionally, in another embodiment, the transceiver unit is furtherconfigured to send downlink channel quality indication information tothe network device, where the downlink channel quality indicationinformation is carried in a Message 3 sent by the terminal device, andthe downlink channel quality indication information is used to indicatedownlink channel quality.

Optionally, in another embodiment, the transceiver unit is specificallyconfigured to send the downlink channel quality indication informationto the network device based on an indication of configurationinformation, where the configuration information is carried in an RARsent by the network device, or the configuration information is carriedin a system message.

Optionally, in another embodiment, the downlink channel qualityindication information includes reference signal received quality RSRQ,or a quantity of NPDCCH repetition times during RAR demodulation by theterminal device.

Therefore, in this embodiment of this application, during levelswitching, the terminal device still sends the preamble by using powerdetermined in a power ramping manner, and a prior-art manner of directlysending a preamble by using maximum power is abandoned. This can reduceimpact on another terminal device. In addition, after the levelswitching, a quantity of repetition times of a preamble during eachtransmission is increased, thereby improving an access successprobability.

Alternatively, the processing unit 910 and the transceiver unit 920 inthe terminal device 900 can further implement the following functions:

the processing unit is configured to control the transceiver unit to:send, to a network device, a random access preamble;

receive a random access response RAR sent by the network device, wherethe RAR indicates a first resource; and

send downlink channel quality indication information to the networkdevice, where the downlink channel quality indication information iscarried in a Message 3 that is sent by the terminal device by using thefirst resource, and the downlink channel quality indication informationis used to indicate downlink channel quality.

Optionally, in another embodiment, the transceiver unit is specificallyconfigured to send the downlink channel quality indication informationto the network device based on configuration information, where theconfiguration information is carried in the RAR sent by the networkdevice, or the configuration information is carried in a system message.

Optionally, in another embodiment, the downlink channel qualityindication information includes reference signal received quality RSRQ,or a quantity of NPDCCH repetition times during RAR demodulation by theterminal device.

Therefore, in this embodiment of this application, the terminal devicereports the downlink channel quality, so that the network device canproperly determine a maximum quantity of repetition times of sending aMessage 4 and/or a maximum value of a USS of the terminal device basedon the downlink channel quality. This resolves an existing problem andavoids excessive power consumption of the terminal device and a systemresource waste, thereby improving network performance.

Alternatively, the processing unit 910 and the transceiver unit 920 inthe terminal device 900 can further implement the following functions:

the processing unit is configured to determine a current coverage levelbased on reference signal receiving performance; and

the transceiver unit is configured to perform random access at thecurrent coverage level.

Optionally, in another embodiment, the processing unit is specificallyconfigured to determine the current coverage level based on thereference signal receiving performance and reference signal receivedpower.

Optionally, in another embodiment, the processing unit is specificallyconfigured to: determine an initial coverage level based on thereference signal received power; and when the initial coverage leveldoes not match the reference signal receiving performance, determine acoverage level corresponding to the reference signal receivingperformance as the current coverage level.

Optionally, in another embodiment, the transceiver unit is specificallyconfigured to send, to the network device, a random access preamble,where transmit power of the preamble is determined based on targetreceived power of the preamble and a path loss between the terminaldevice and the network device, and the target received power of thepreamble is related to a current power ramp step and a current quantityof times of sending the preamble by the terminal device.

Optionally, in another embodiment, the transmit power of the preamble isdetermined according to the following formula:

P _(NPRACH)=min{P _(CMAX) , P _(TARGET) +PL} [dBM], where

P_(NPRACH) represents the transmit power of the preamble, P_(CMAX)represents maximum transmit power of the terminal device, P_(TARGET)represents the target received power of the preamble, and PL representsthe path loss, where

P _(TARGET) P _(P)+(M−1) P_(S), where

P_(TARGET)=P_(P)+(M−1) P_(S), where

P_(P) represents initial target received power of the preamble, Mrepresents the current quantity of sending times, and P_(S) representsthe power ramp step; or

P_(TARGET)=P_(P)+(M−1) P_(S)−10×log₁₀N_(r), where N_(r) is a quantity ofrepetition times of sending the preamble.

Therefore, in this embodiment of this application, the terminal devicemay determine the current coverage level based on the reference signalreceiving performance, so that the current coverage level can beflexibly and accurately determined, improving network performance.

Alternatively, the processing unit 910 and the transceiver unit 920 inthe terminal device 900 can further implement the following functions:

the terminal device receives indication information sent by a networkdevice, where the indication information is used to indicate a quantityof repetition times of sending uplink information by the terminaldevice; and

when the terminal device determines that the quantity of repetitiontimes is greater than a second threshold, the terminal device sends theuplink information by using maximum transmit power; or

when the terminal device determines that the quantity of repetitiontimes is less than or equal to the second threshold, the terminal devicesends the uplink information by using first power, where the first poweris determined by the terminal device based on at least one of a pathloss, a path loss compensation factor, or transmission bandwidth.

Optionally, in another embodiment, the indication information is carriedin an uplink grant UL grant, and the uplink information is uplink data;or

the indication information is carried in a random access response RAR,and the uplink information is a Message 3.

Optionally, in another embodiment, the second threshold is preset, thesecond threshold is indicated by the RAR, or the second threshold isconfigured by using a system message.

Therefore, in this embodiment of this application, because the specifiedsecond threshold is greater than 2, even if a quantity of repetitiontimes configured by the network device for the Message 3 is greater than2, the terminal device may send the Message 3 by using, for example, thefirst power instead of the maximum power, provided that the quantity ofrepetition times is less than the second threshold, so as to reduce anoise floor of the network device and reduce impact on another terminaldevice, thereby improving network performance.

It should be understood that the terminal device 900 shown in FIG. 9 canimplement the processes corresponding to the terminal device in themethod embodiments in FIG. 1 to FIG. 9. Operations and/or functions ofeach module in the terminal device are intended to implement respectivecorresponding procedures in the method embodiments in FIG. 1 to FIG. 9.For details, refer to descriptions in the method embodiments. To avoidrepetition, detailed descriptions are omitted as appropriate herein.

FIG. 10 is a schematic block diagram of a network device 1000 accordingto an embodiment of this application. Specifically, as shown in FIG. 10,the network device 1000 includes a processing unit 1010 and atransceiver unit 1020.

Specifically, the processing unit is configured to control thetransceiver unit to: send a reference signal to a terminal device, sothat the terminal device determines a current coverage level from atleast two coverage levels based on reference signal received power,where each of the at least two coverage levels is corresponding to apower ramp step; and receive a random access preamble, where thepreamble is sent by the terminal device in a power ramping manner basedon a current power ramp step corresponding to the current coveragelevel.

Therefore, in this embodiment of this application, the terminal devicesends the preamble at the current level by using power determined in apower ramping manner, and a prior-art manner of directly sending apreamble by using maximum power is abandoned. This can reduce impact onanother terminal device.

Optionally, in another embodiment, the transceiver unit is furtherconfigured to: send indication information to the terminal device, wherethe indication information is used to indicate a quantity of repetitiontimes of sending uplink information by the terminal device; and

receive the uplink information, where when the quantity of repetitiontimes is greater than a second threshold, the uplink information is sentby the terminal device by using maximum transmit power; or

when the quantity of repetition times is less than or equal to thesecond threshold, the uplink information is sent by the terminal deviceby using first power, where the first power is determined by theterminal device based on at least one of a path loss, a path losscompensation factor, or transmission bandwidth.

Optionally, in another embodiment, the indication information is carriedin an uplink grant UL grant, and the uplink information is uplink data;or

the indication information is carried in a random access response RAR,and the uplink information is a Message 3.

Optionally, in another embodiment, the second threshold is preset, thesecond threshold is indicated by the RAR, or the second threshold isconfigured by using a system message.

Optionally, in another embodiment, the transceiver unit is furtherconfigured to receive downlink channel quality indication informationsent by the terminal device, where the downlink channel qualityindication information is carried in a Message 3 that is sent by theterminal device and that is received by the network device, and thedownlink channel quality indication information is used to indicatedownlink channel quality; and

the processing unit is further configured to determine a maximumquantity of repetition times of sending a Message 4 and/or a maximumvalue of a USS of the terminal device based on the downlink channelquality.

Optionally, in another embodiment, the downlink channel qualityindication information is sent by the terminal device based on anindication of configuration information, where the configurationinformation is carried in an RAR sent by the transceiver unit, or theconfiguration information is carried in a system message.

Optionally, in another embodiment, the downlink channel qualityindication information includes reference signal received quality RSRQ,or a quantity of NPDCCH repetition times during RAR demodulation by theterminal device.

Alternatively, the processing unit 1010 and the transceiver unit 1020 inthe network device 1000 can further implement the following functions:

the transceiver unit is configured to: receive a random access preamblesent by a terminal device;

send a random access response RAR to the terminal device, where the RARindicates a first resource; and

receive downlink channel quality indication information sent by theterminal device, where the downlink channel quality indicationinformation is carried in a Message 3 that is sent by the terminaldevice by using the first resource, and the downlink channel qualityindication information is used to indicate downlink channel quality; and

the processing unit is configured to determine a maximum quantity ofrepetition times of sending a Message 4 and/or a maximum value of a USSof the terminal device based on the downlink channel quality.

Optionally, in another embodiment, the downlink channel qualityindication information is sent by the terminal device based on anindication of configuration information, where the configurationinformation is carried in the RAR sent by the transceiver unit, or theconfiguration information is carried in a system message.

Optionally, in another embodiment, the downlink channel qualityindication information includes reference signal received quality RSRQ,or a quantity of NPDCCH repetition times during RAR demodulation by theterminal device.

Therefore, in this embodiment of this application, the terminal devicereports the downlink channel quality, so that the network device canproperly determine the maximum quantity of repetition times of sendingthe Message 4 and/or the maximum value of the USS of the terminal devicebased on the downlink channel quality. This resolves an existing problemand avoids excessive power consumption of the terminal device and asystem resource waste, thereby improving network performance.

Alternatively, the processing unit 1010 and the transceiver unit 1020 inthe network device 1000 can further implement the following functions:

the processing unit is configured to control the transceiver unit to:send indication information to a terminal device, where the indicationinformation is used to indicate a quantity of repetition times ofsending uplink information by the terminal device; and

receive the uplink information, where when the quantity of repetitiontimes is greater than a second threshold, the uplink information is sentby the terminal device by using maximum transmit power; or when thequantity of repetition times is less than or equal to the secondthreshold, the uplink information is sent by the terminal device byusing first power, where the first power is determined by the terminaldevice based on at least one of a path loss, a path loss compensationfactor, or transmission bandwidth.

Optionally, in another embodiment, the indication information is carriedin an uplink grant UL grant, and the uplink information is uplink data;or the indication information is carried in a random access responseRAR, and the uplink information is a Message 3.

Optionally, in another embodiment, the second threshold is preset, thesecond threshold is indicated by the RAR, or the second threshold isconfigured by using a system message.

Therefore, in this embodiment of this application, because the specifiedsecond threshold is greater than 2, even if a quantity of repetitiontimes configured by the network device for the Message 3 is greater than2, the terminal device may send the Message 3 by using, for example, thefirst power instead of the maximum power, provided that the quantity ofrepetition times is less than the second threshold, so as to reduce anoise floor of the network device and reduce impact on another terminaldevice, thereby improving network performance.

It should be understood that the network device 1000 shown in FIG. 10can implement the processes corresponding to the network device in themethod embodiments in FIG. 1 to FIG. 9. Operations and/or functions ofeach module in the network device are intended to implement respectivecorresponding procedures in the method embodiments in FIG. 1 to FIG. 9.For details, refer to descriptions in the method embodiments. To avoidrepetition, detailed descriptions are omitted as appropriate herein.

FIG. 11 is a schematic block diagram of a terminal device 1100 accordingto an embodiment of this application. Specifically, as shown in FIG. 11,the terminal device 1100 includes a processor 1110 and a transceiver1120, where the processor 1110 is connected to the transceiver 1120.Optionally, the terminal device 1100 further includes a memory 1130,where the memory 1130 is connected to the processor 1110. The processor1110, the memory 1130, and the transceiver 1120 communicate with eachother by using an internal connection path, to transfer a control signaland/or a data signal. The memory 1130 may be configured to store aninstruction. The processor 1110 is configured to: execute theinstruction stored in the memory 1130, and control the transceiver 1120to receive and send information or signals. The processor 1110 executesthe instruction in the memory 1130, so that the processes correspondingto the terminal device in the method embodiments in FIG. 1 to FIG. 8 canbe completed. To avoid repetition, details are not described hereinagain.

It should be understood that, the terminal device 1100 may becorresponding to the terminal device 900 in FIG. 9, functions of theprocessing unit 910 in the terminal device 900 may be implemented by theprocessor 1110, and functions of the transceiver unit 920 may beimplemented by the transceiver 1120.

Therefore, in this embodiment of this application, the terminal devicesends the preamble at the current level by using power determined in apower ramping manner, and a prior-art manner of directly sending apreamble by using maximum power is abandoned. This can reduce impact onanother terminal device.

FIG. 12 is a schematic block diagram of a network device 1200 accordingto an embodiment of this application. Specifically, as shown in FIG. 12,the network device 1200 includes a processor 1210 and a transceiver1220, where the processor 1210 is connected to the transceiver 1220.Optionally, the network device 1200 further includes a memory 1230,where the memory 1230 is connected to the processor 1210. The processor1210, the memory 1230, and the transceiver 1220 communicate with eachother by using an internal connection path, to transfer a control signaland/or a data signal. The memory 1230 may be configured to store aninstruction. The processor 1210 is configured to: execute theinstruction stored in the memory 1230, and control the transceiver 1220to receive and send information or signals. The processor 1210 executesthe instruction in the memory 1230, so that the processes correspondingto the network device in the method embodiments in FIG. 2 to FIG. 9 canbe completed. To avoid repetition, details are not described hereinagain.

It should be understood that, the network device 1200 may becorresponding to the network device 1000 in FIG. 10, functions of theprocessing unit 1010 in the network device 1000 may be implemented bythe processor 1210, and functions of the transceiver unit 1020 may beimplemented by the transceiver 1220.

Therefore, in this embodiment of this application, the terminal devicesends the preamble at the current level by using power determined in apower ramping manner, and a prior-art manner of directly sending apreamble by using maximum power is abandoned. This can reduce impact onanother terminal device.

It should be noted that the processor (for example, the processor 1210in FIG. 12 or the processor 1110 in FIG. 11) in the embodiments of thisapplication may be an integrated circuit chip having a signal processingcapability. In an implementation process, steps in the foregoing methodembodiments may be implemented by using a hardware integrated logicalcircuit in the processor, or by using an instruction in a form ofsoftware. The processor may be a general purpose processor, a digitalsignal processor (digital signal processor, DSP), anapplication-specific integrated circuit (application-specific integratedcircuit, ASIC), a field programmable gate array (field programmable gatearray, FPGA) or another programmable logic device, a discrete gate or atransistor logic device, or a discrete hardware component. The processormay implement or perform the methods, steps, and logical block diagramsthat are disclosed in the embodiments of this application. The generalpurpose processor may be a microprocessor, or the processor may be anyconventional processor or the like. Steps in the methods disclosed withreference to the embodiments of this application may be directlyexecuted and accomplished by using a hardware decoding processor, or maybe executed and accomplished by using a combination of hardware in adecoding processor and a software module. The software module may belocated in a mature storage medium in the art, such as a random accessmemory, a flash memory, a read-only memory, a programmable read-onlymemory, an electrically erasable programmable memory, or a register. Thestorage medium is located in the memory, and the processor readsinformation from the memory and completes the steps in the foregoingmethods in combination with hardware of the processor.

It may be understood that the memory (such as the memory 1230 in FIG. 12or the memory 1130 in FIG. 11) in the embodiments of this applicationmay be a volatile memory or a nonvolatile memory, or may include both avolatile memory and a nonvolatile memory. The nonvolatile memory may bea read-only memory (read-only memory, ROM), a programmable read-onlymemory (programmable ROM, PROM), an erasable programmable read-onlymemory (erasable PROM, EPROM), an electrically erasable programmableread-only memory (electrically EPROM, EEPROM), or a flash memory. Thevolatile memory may be a random access memory (random access memory,RAM), used as an external cache. By way of example but not limitativedescription, many forms of RAMs may be used, for example, a staticrandom access memory (static RAM, SRAM), a dynamic random access memory(dynamic RAM, DRAM), a synchronous dynamic random access memory(synchronous DRAM, SDRAM), a double data rate synchronous dynamic randomaccess memory (double data rate SDRAM, DDR SDRAM), an enhancedsynchronous dynamic random access memory (enhanced SDRAM, ESDRAM), asynchlink dynamic random access memory (synchlink DRAM, SLDRAM), and adirect rambus dynamic random access memory (direct rambus RAM, DR RAM).It should be noted that the memory of the systems and methods describedin this specification includes but is not limited to these memories andany memory of another proper type.

An embodiment of this application further provides a computer-readablemedium.

The computer-readable medium stores a computer program, and when thecomputer program is executed by a computer, the communication method inany one of the foregoing method embodiments is implemented.

An embodiment of this application further provides a computer programproduct. When the computer program product is executed by a computer,the communication method in any one of the foregoing method embodimentsis implemented.

The foregoing embodiments may be completely or partially implemented byusing software, hardware, firmware, or any combination thereof. When theembodiment is implemented by using software, the embodiment may beimplemented completely or partially in a form of a computer programproduct. The computer program product includes one or more computerinstructions. When the computer instruction is loaded and executed on acomputer, all or some of the procedure or functions according to theembodiments of this application are generated. The computer may be ageneral purpose computer, a dedicated computer, a computer network, oranother programmable apparatus. The computer instruction may be storedin a computer-readable storage medium, or may be transmitted from acomputer-readable storage medium to another computer-readable storagemedium. For example, the computer instruction may be transmitted from awebsite, computer, server, or data center to another website, computer,server, or data center in a wired (for example, a coaxial cable, anoptical fiber, or a digital subscriber line (digital subscriber line,DSL)) or wireless (for example, infrared, radio, or microwave) manner.The computer-readable storage medium may be any usable medium accessibleto a computer, or a data storage device, such as a server or a datacenter, integrating one or more usable media. The usable medium may be amagnetic medium (for example, a floppy disk, a hard disk, or a magnetictape), an optical medium (for example, a high-density digital video disc(digital video disc, DVD)), a semiconductor medium (for example, a solidstate drive (solid state disk, SSD)), or the like.

It should be understood that the processing apparatus may be a chip, andthe processor may be implemented by using hardware or software. When theprocessor is implemented by using hardware, the processor may be a logiccircuit, an integrated circuit, or the like. When the processor isimplemented by using software, the processor may be a general purposeprocessor, and is implemented by reading software code stored in amemory. The memory may be integrated into the processor, or may belocated outside the processor, and exist independently.

It should be understood that sequence numbers of the foregoing processesdo not mean execution sequences in various embodiments of thisapplication. The execution sequences of the processes should bedetermined based on functions and internal logic of the processes, andshould not be construed as any limitation on the implementationprocesses of the embodiments of this application.

In addition, the terms “system” and “network” may usually be usedinterchangeably in this specification. The term “and/or” in thisspecification describes only an association relationship for describingassociated objects and represents that three relationships may exist.For example, A and/or B may represent the following three cases: Only Aexists, both A and B exist, and only B exists. In addition, thecharacter “/” in this specification generally indicates an “or”relationship between the associated objects.

It should be understood that, in the embodiments of this application, “Bcorresponding to A” indicates that B is associated with A, and B may bedetermined according to A. However, it should also be understood thatdetermining B according to A does not mean that B is determined onlyaccording to A, but B may alternatively be determined according to Aand/or other information.

A person of ordinary skill in the art may be aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps can be implemented by usingelectronic hardware, computer software, or a combination thereof. Toclearly describe interchangeability between the hardware and thesoftware, the foregoing generally describes compositions and steps ofeach example based on functions. Whether the functions are performed byhardware or software depends on particular applications and designconstraints of the technical solutions. A person skilled in the art mayuse a different method to implement the described functions for eachparticular application, but it should not be considered that theimplementation goes beyond the scope of this application.

It may be clearly understood by a person skilled in the art that, forthe purpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, reference may bemade to a corresponding process in the foregoing method embodiments.Details are not described herein again.

In addition, functional units in the embodiments of this application maybe integrated into one processing unit, or each of the units may existalone physically, or at least two units are integrated into one unit.The integrated unit may be implemented in a form of hardware, or may beimplemented in a form of a software functional unit.

With descriptions of the foregoing implementations, a person skilled inthe art may clearly understand that this application may be implementedby using hardware, firmware, or a combination thereof. When thisapplication is implemented by using software, the foregoing functionsmay be stored in a computer-readable medium or transmitted as one ormore instructions or code in the computer-readable medium. Thecomputer-readable medium includes a computer storage medium and acommunications medium, where the communications medium includes anymedium that enables a computer program to be transmitted from one placeto another. The storage medium may be any usable medium accessible to acomputer. The following provides an example but does not impose anylimitation: The computer-readable medium may include a RAM, a ROM, anEEPROM, a CD-ROM, other optical disc storage, a magnetic disk storagemedium, another magnetic storage device, or any other medium that cancarry or store expected program code in a form of an instruction or adata structure and that is accessible to a computer. In addition, anyconnection may be appropriately defined as a computer-readable medium.For example, if software is transmitted from a website, a server, oranother remote source by using a coaxial cable, an optical fiber/cable,a twisted pair, a digital subscriber line (DSL), or wirelesstechnologies such as infrared ray, radio, and microwave, the coaxialcable, optical fiber/cable, twisted pair, DSL, or wireless technologiessuch as infrared ray, radio, and microwave are included in fixation of amedium to which they belong. For example, a disk (disk) or a disc (disc)used in this application includes a compact disc (CD), a laser disc, anoptical disc, a digital versatile disc (DVD), a floppy disk, and aBlu-ray disc, where the disk generally copies data by a magnetic means,and the disc copies data optically by using a laser. The foregoingcombination should also be included in the protection scope of thecomputer-readable medium.

In sum, the foregoing descriptions are merely examples of theembodiments of the technical solutions of this application, but are notintended to limit the protection scope of this application. Anymodification, equivalent replacement, or improvement made withoutdeparting from the spirit and principle of this application shall fallwithin the protection scope of this application.

In the claims:
 1. A communication method, comprising: sending, by anetwork device, a system message to a terminal device, wherein thesystem message carries configuration information indicating sending ofdownlink channel quality indication information; receiving, by theterminal device, the system message from the network device; sending, bythe terminal device to the network device, a random access preamble;receiving, by the network device, the random access preamble from theterminal device; sending, by the network device, a random accessresponse (RAR) to the terminal device, wherein the RAR indicates a firstresource; receiving, by the terminal device, the RAR from the networkdevice; and sending, by the terminal device, the downlink channelquality indication information to the network device based on theconfiguration information, wherein the downlink channel qualityindication information is carried in a Message 3 on the first resource,the downlink channel quality indication information indicates downlinkchannel quality, and the downlink channel quality indication informationcomprises a quantity of narrowband physical downlink control channel(NPDCCH) repetition times associated with RAR demodulation; andreceiving, by the network device, the downlink channel qualityindication information from the terminal device.
 2. The method accordingto claim 1, further comprises: determining, by the network device, amaximum value of a UE-specific search space (USS) of the terminal devicebased on the downlink channel quality.
 3. The method according to claim1, further comprises: determining, by the terminal device, a currentcoverage level from at least two coverage levels, wherein each of the atleast two coverage levels corresponds to a power ramp step; and whereinthe sending, by the terminal device to the network device, the randomaccess preamble, comprises: sending the random access preamble in apower ramping manner based on a current power ramp step corresponding tothe current coverage level.
 4. The method according to claim 3, whereinthe sending the random access preamble in the power ramping manner basedon the current power ramp step corresponding to the current coveragelevel, comprises: in response to failing in sending the preamble,increasing, by the terminal device, transmit power of the preamble bythe current power ramp step, to obtain new transmit power; andresending, by the terminal device, the preamble by using the newtransmit power.
 5. The method according to claim 3, wherein the methodfurther comprises: in response to a quantity of times of sending thepreamble by the terminal device at the current coverage level is greaterthan a first threshold, sending, by the terminal device, the preamble tothe network device at a next coverage level of the current coveragelevel, wherein the first threshold is less than a maximum quantity oftimes of transmitting a preamble at the current coverage level.
 6. Themethod according to claim 5, wherein the sending, by the terminaldevice, the preamble to the network device at the next coverage level ofthe current coverage level comprises: sending, by the terminal device,the preamble in a power ramping manner by using a quantity of repetitiontimes corresponding to the next coverage level and the current powerramp step corresponding to the current coverage level.
 7. Acommunication system, comprising: a network device and a terminaldevice, wherein the network device comprises: at least one firstprocessor; and one or more first memories coupled to the at least onefirst processor and storing first programming instructions for executionby the at least one first processor to cause the network device to: senda system message to the terminal device, wherein the system messagecarries configuration information indicating sending of downlink channelquality indication information; receive a random access preamble fromthe terminal device; send a random access response (RAR) to the terminaldevice, wherein the RAR indicates a first resource; and receive thedownlink channel quality indication information from the terminaldevice, wherein the downlink channel quality indication information iscarried in a Message 3 on the first resource, the downlink channelquality indication information is used to indicate downlink channelquality, and the downlink channel quality indication informationcomprises a quantity of narrowband physical downlink control channel(NPDCCH) repetition times associated with RAR demodulation; and whereinthe terminal device comprises: at least one second processor; and one ormore second memories coupled to the at least one second processor andstoring second programming instructions for execution by the at leastone second processor to cause the terminal device to: receive the systemmessage from the network device; send, to the network device, the randomaccess preamble; receive the RAR from the network device; and send thedownlink channel quality indication information to the network devicebased on the configuration information.
 8. The system according to claim7, wherein the first programming instructions, when executed by the atleast one first processor, cause the network device to: determine amaximum value of a UE-specific search space (USS) of the terminal devicebased on the downlink channel quality.
 9. The system according to claim7, wherein the second programming instructions, when executed by the atleast one second processor, cause the terminal device to: determine acurrent coverage level from at least two coverage levels, wherein eachof the at least two coverage levels corresponds to a power ramp step;and send the random access preamble in a power ramping manner based on acurrent power ramp step corresponding to the current coverage level. 10.The system according to claim 9, wherein second programminginstructions, when executed by the at least one second processor, causethe terminal device to: in response to failing in sending the preamble,increase transmit power of the preamble by the current power ramp step,to obtain new transmit power; and resend the preamble by using the newtransmit power.
 11. The system according to claim 9, wherein the secondprogramming instructions, when executed by the at least one secondprocessor, cause the terminal device to: in response to a quantity oftimes of sending the preamble by the terminal device at the currentcoverage level is greater than a first threshold, send the preamble tothe network device at a next coverage level of the current coveragelevel, wherein the first threshold is less than a maximum quantity oftimes of transmitting a preamble at the current coverage level.
 12. Thesystem according to claim 11, wherein the second programminginstructions, when executed by the at least one second processor, causethe terminal device to: send the preamble in a power ramping manner byusing a quantity of repetition times corresponding to the next coveragelevel and the current power ramp step corresponding to the currentcoverage level.
 13. A communication method, comprising: sending, by anetwork device, a system message to a terminal device, wherein thesystem message carries configuration information indicating sending ofdownlink channel quality indication information; receiving, by thenetwork device, a random access preamble from the terminal device;sending, by the network device, a random access response (RAR) to theterminal device, wherein the RAR indicates a first resource; andreceiving, by the network device, the downlink channel qualityindication information from the terminal device, wherein the downlinkchannel quality indication information is carried in a Message 3 on thefirst resource, the downlink channel quality indication information isused to indicate downlink channel quality, and the downlink channelquality indication information comprises a quantity of narrowbandphysical downlink control channel (NPDCCH) repetition times associatedwith RAR demodulation.
 14. The method according to claim 13, furthercomprises: determining, by the network device, a maximum value of aUE-specific search space (USS) of the terminal device based on thedownlink channel quality.
 15. An apparatus, comprising: at least oneprocessor; and a non-transitory memory coupled to the at least oneprocessor and storing programming instructions for execution by the atleast one processor to cause the apparatus to: send a system message toa terminal device, wherein the system message carries configurationinformation indicating sending of downlink channel quality indicationinformation; receive a random access preamble from the terminal device;send a random access response (RAR) to the terminal device, wherein theRAR indicates a first resource; and receive the downlink channel qualityindication information from the terminal device, wherein the downlinkchannel quality indication information is carried in a Message 3 on thefirst resource, the downlink channel quality indication information isused to indicate downlink channel quality, and the downlink channelquality indication information comprises a quantity of narrowbandphysical downlink control channel (NPDCCH) repetition times associatedwith RAR demodulation.
 16. The apparatus according to claim 15, whereinthe non-transitory memory stores programming instructions for executionby the at least one processor to: determine a maximum value of aUE-specific search space (USS) of the terminal device based on thedownlink channel quality.
 17. The method according to claim 1, furthercomprises: determining, by the network device, a maximum quantity ofrepetition times of sending a Message 4 or a maximum value of aUE-specific search space (USS) of the terminal device based on thedownlink channel quality.
 18. The system according to claim 7, whereinthe first programming instructions, when executed by the at least onefirst processor, cause the network device to: determine a maximumquantity of repetition times of sending a Message 4 or a maximum valueof a UE-specific search space (USS) of the terminal device based on thedownlink channel quality.
 19. The method according to claim 13, furthercomprises: determining, by the network device, a maximum quantity ofrepetition times of sending a Message 4 or a maximum value of aUE-specific search space (USS) of the terminal device based on thedownlink channel quality.
 20. The apparatus according to claim 15,wherein the non-transitory memory stores programming instructions forexecution by the at least one processor to: determine a maximum quantityof repetition times of sending a Message 4 or a maximum value of aUE-specific search space (USS) of the terminal device based on thedownlink channel quality.